Cleaned up role.

docker-playbook.yml

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+---
+- name: Call the docker role.
+  hosts: all
+  roles:
+    - {role: install_docker, docker_users: [admin]}

roles/install_docker/README.md

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+Ansible Role: Install Docker
+================================================================================
+
+An Ansible role that installs Docker.
+
+This role has been tested on:
+- Amazon Linux 2
+- ArchLinux
+- Centos 7 & 8
+- Ubuntu 20.04
+
+Variables
+----------------------------------------
+
+The variable that you're most likely going to want to change is `docker_users`.
+That variable is a list of all the users on the system that should be added to
+the `docker` group.
+```yml
+docker_users: [ admin, docker_admin ]
+```
+
+Example Playbook
+----------------
+
+```yml
+- hosts: k8s-nodes
+  roles:
+    - {role: install_docker, docker_users: [admin]}
+```
+
+License
+-------
+
+MIT
+
+Author Information
+------------------
+
+This role was created by [shnee](github.com/shnee).

roles/install_docker/defaults/main.yml

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+---
+# A list of users to be added to the docker group.
+docker_users: []
+
+centos_repo_file: docker-ce.repo
+centos_repo_full_path: "/etc/yum.repos.d/{{ centos_repo_file }}"
+centos_repo_url: "https://download.docker.com/linux/centos/\
+                  {{ centos_repo_file }}"
+
+ubuntu_docker_base_url: https://download.docker.com/linux/ubuntu
+ubuntu_gpg_url: "{{ ubuntu_docker_base_url }}/gpg"
+ubuntu_gpg_fingerprint: 9DC858229FC7DD38854AE2D88D81803C0EBFCD88
+ubuntu_apt_repo: >
+  deb [arch=amd64]
+  "{{ ubuntu_docker_base_url }}"
+  "{{ ansible_distribution_release }}"
+  stable

roles/install_docker/meta/main.yml

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+---
+dependencies: []
+
+galaxy_info:
+  author: shnee
+  description: Install docker.
+
+  license: MIT
+
+  min_ansible_version: 2.1
+
+  platforms:
+    - name: ArchLinux
+      versions:
+        - all
+    - name: Amazon Linux 2
+      versions:
+        - all
+    - name: Ubuntu
+        - focal  # 20.04
+    # CentOS is apparently not in https://galaxy.ansible.com/api/v1/platforms/
+
+  galaxy_tags:
+    - containers
+    - docker

roles/install_docker/tasks/main.yml

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+---
+# This has only been tests on Amazon Linux 2, CentOS 7-8, Ubuntu 20.04, and
+# ArchLinux.
+
+# Prequisites
+# This step will:
+# 1. Remove any unwanted docker packages, (we want newest package from official
+#    docker repos.
+# 2. Install dependencies.
+# 3. Add official docker repo.
+
+# Archlinux and Amazon Linux don't have any prequisite steps, they're
+# repositories have up to date docker packages so we don't need to add a 3rd
+# party repo or uninstall unwanted packages.
+
+- include_tasks: prereq_centos.yml
+  when: ansible_distribution == "CentOS"
+
+- include_tasks: prereq_ubuntu.yml
+  when: ansible_distribution == "Ubuntu"
+
+# The arch cloud image does not have a package cache.
+- include_tasks: update_arch.yml
+  when: ansible_distribution == "Archlinux"
+
+- name: Install docker packages after adding 3rd party repo.
+  package:
+    name:
+      - docker-ce
+      - docker-ce-cli
+      - containerd.io
+    state: present
+  become: true
+  when: ansible_distribution != "Amazon" and ansible_distribution != "Archlinux"
+- name: Install docker packages for distros that don't use a 3rd party repo.
+  package:
+    name:
+      - docker
+    state: present
+  become: true
+  when: ansible_distribution == "Amazon" or ansible_distribution == "Archlinux"
+
+- name: Add users to the docker group.
+  user:
+    name: "{{ item }}"
+    groups:
+      - docker
+    append: true
+  with_items: "{{ docker_users }}"
+  become: true
+
+- name: Enable and start docker service.
+  service:
+    name: docker
+    state: started
+    enabled: true
+  become: true

roles/install_docker/tasks/prereq_centos.yml

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+---
+# This commented out code was an attempt to make sure the CentOS extras repo is
+# enabled.
+# TODO This isn't working. It will create the repo everytime regardless whether
+# or not the repo is already enabled. For now we leave it because this repo is
+# enabled by defaullt on CentOS 7 & 8
+#
+# https://docs.docker.com/engine/install/centos/#os-requirements
+# Look in /etc/yum.repos.d/ for examples of the fields for a repo. This files
+# have variables in their config. To get the values of the variables you can
+# run:
+# `python -c 'import yum; yb = yum.YumBase(); print(yb.conf.yumvar)'`
+# - name: Ensure CentOS extras repo is enbaled for CentOS 7.
+#   yum_repository:
+#     name: extras
+#     description: CentOS-{{ ansible_distribution_major_version }} - Extras
+#     enabled: true
+#     mirrorlist: "http://mirrorlist.centos.org/?\
+#                  release={{ ansible_distribution_major_version }}&\
+#                  arch={{ ansible_architecture }}&\
+#                  repo=extras&infra=genclo"
+#     gpgcheck: true
+#   become: true
+#   when: >
+#       ansible_distribution == "CentOS" and
+#       ansible_distribution_major_version == "7"
+# - name: Ensure CentOS extras repo is enbaled for CentOS 8.
+#   yum_repository:
+#     name: extras
+#     description: >
+#       CentOS Linux {{ ansible_distribution_major_version }} - Extras
+#     enabled: true
+#     mirrorlist: "http://mirrorlist.centos.org/?\
+#                  release={{ ansible_distribution_major_version }}&\
+#                  arch={{ ansible_architecture }}&\
+#                  repo=extras&infra=genclo"
+#     gpgcheck: true
+#   become: true
+#   when: >
+#       ansible_distribution == "CentOS" and
+#       ansible_distribution_major_version == "8"
+
+# TODO Add this step.
+# https://docs.docker.com/engine/install/centos/#os-requirements
+
+################################################################################
+# Uninstall unwanted docker packages.
+################################################################################
+
+# This step combines "Uninstall old versions" for RedHat family distros.
+# https://docs.docker.com/engine/install/centos/#uninstall-old-versions
+# https://docs.docker.com/engine/install/fedora/#uninstall-old-versions
+# https://docs.docker.com/engine/install/rhel/#uninstall-old-versions
+
+# We check if a docker repo has alredy been added to yum. If so, then we want to
+# skip the removing of the old docker packages to make this script more
+# idempotent.
+- name: Check if docker repo has alredy been added.
+  command: yum repolist  # noqa command-instead-of-module
+  changed_when: false
+  register: repolist
+
+- name: Uninstall old versions of docker RedHat like distros..
+  yum:
+    name:
+      - docker
+      - docker-client
+      - docker-client-latest
+      - docker-common
+      - docker-latest
+      - docker-latest-logrotate
+      - docker-logrotate
+      - docker-selinux
+      - docker-engine-selinux
+      - docker-engine
+      - podman
+      - runc
+    state: absent
+  become: true
+  when: "'docker' not in repolist.stdout"
+
+################################################################################
+# Install dependencies
+################################################################################
+
+# https://docs.docker.com/engine/install/centos/#install-using-the-repository
+- name: Install dependencies for yum distros.
+  yum:
+    name:
+      - yum-utils
+    state: present
+  become: true
+
+################################################################################
+# Install docker repo.
+################################################################################
+
+# https://docs.docker.com/engine/install/centos/#install-using-the-repository
+- name: Add docker yum repo for centos.
+  command:
+    cmd: "yum-config-manager --add-repo {{ centos_repo_url }}"
+    creates: "{{ centos_repo_full_path }}"
+  become: true

roles/install_docker/tasks/prereq_ubuntu.yml

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+---
+################################################################################
+# Uninstall unwanted docker packages.
+################################################################################
+
+# https://docs.docker.com/engine/install/ubuntu/#uninstall-old-versions
+- name: Remove old docker packages for Debian like distros.
+  apt:
+    name:
+      - docker
+      - docker-engine
+      - docker.io
+      - containerd
+      - runc
+    state: absent
+  become: true
+
+################################################################################
+# Install dependencies
+################################################################################
+
+# https://docs.docker.com/engine/install/ubuntu/#install-using-the-repository
+- name: Install Docker dependencies on Debian like distro.
+  apt:
+    name:
+      - ca-certificates
+      - curl
+      - gnupg
+      - lsb-release
+  become: true
+
+################################################################################
+# Install docker repo.
+################################################################################
+
+# https://docs.docker.com/engine/install/ubuntu/#install-using-the-repository
+- name: Add GPG key to apt for Ubuntu.
+  apt_key:
+    url: "{{ ubuntu_gpg_url }}"
+    id: "{{ ubuntu_gpg_fingerprint }}"
+    state: present
+  become: true
+
+# https://docs.docker.com/engine/install/ubuntu/#install-using-the-repository
+- name: Add Docker repository for Ubuntu.
+  apt_repository:
+    repo: "{{ ubuntu_apt_repo }}"
+    state: present
+    update_cache: true
+  become: true

roles/install_docker/tasks/update_arch.yml

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+---
+# These tasks will update the pacman repos if Docker is not alredy instflled.
+#
+# We only want to update the chache if needed, otherwise this will break
+# idempotentcy.
+
+- name: Get a list of installed pacakges.
+  ansible.builtin.package_facts:
+    manager: auto
+
+- name: Update pacman cache if docker is not installed.
+  pacman:
+    update_cache: true
+  become: true
+  when: "'docker' not in ansible_facts.packages"